Continuous colorimetric determination of trace ammonium in seawater with a long-path liquid waveguide capillary cell

An automated method for routine determination of nanomolar ammonium in seawater has been developed using segmented flow analysis coupled with a 2-m-long liquid waveguide capillary cell. Conventional photometric detector and autosampler were modified for this method. The optimal concentrations of the reagents and parameters for the development of indophenol blue are discussed. The method has low detection limit (5 nM), high precision (5% at 10-100 nM) and the advantage of rapid analysis of a large number of samples. The method has been used to examine the distribution of ammonium in Florida Bay and Biscayne Bay.